This invention relates generally to a hydraulic drive system and elements thereof which may be used for actuating devices having multiple operations, such as a chair having both lift and tilt features.
Hydraulic drive systems are used in many operations for powering multiple actions. Examples of such are power actuated chairs, such as dental chairs, which often are operated by pressurized hydraulic fluid systems in which one hydraulic cylinder, or ram, is operable to raise the chair, and a second hydraulic cylinder, or ram, is operable to tilt the chair or a portion thereof. Many prior hydraulic drive systems have been disclosed in the past, but each has had disadvantages.
Some prior systems use drive pumps, motor units, and control circuits which produce movement of the item to be driven in a manner which is not as smooth as may be desired. In a hydraulically actuated chair, for example, prior systems may produce movement which is too fast, too slow, or may produce jerking start and stop actuation which is uncomfortable for the user.
Prior systems also have been constructed in such a manner that they are more complex and expensive than may be desired to fulfill their functions. Often prior systems have been produced in such a manner that they require an undesirable number of actuating valves and are produced in a generally open architecture of hoses and connections which are subject to breakage and leakage.
An object of the present disclosure is to provide a novel, efficient, and economically produced hydraulic drive system.
Another object is to provide a hydraulic drive system which produces smooth operation of driven components actuated by the system.
More specifically, an object is to provide a hydraulic drive system such as is used to drive raising and tilting cylinders for a chair, such as a dental chair, in such a manner as to provide comfortable starting, stopping, and intermediate operation for a party carried in the chair.
Another object is to provide a system in which a bi-directional crescent gear pump drive is used to provide a substantially pulseless supply of pressurized fluid, with actuation of the pump in one direction providing pressurized fluid to one ram in the system, and actuation of the pump in the opposite direction providing pressurized fluid to the other ram in the system. Recognizing that more power is required for a chair lift ram than for a chair tilting ram, an electric drive motor for the pump may be used which is capable of producing greater torque in one direction than in the reverse direction, such that it may drive the pump in the direction of greater torque output to produce lifting of the chair, and may drive the pump in the reverse, lower powered, direction of the motor for producing tilting.
A still further object of the present disclosure is to provide a novel hydraulic drive system in which a minimum number of hydraulic circuit control components are required.
Yet another object is to provide a novel hydraulic drive system in which a monolithic body has a plurality of bores formed therein which extend inwardly from external surface regions of the body but do not extend fully through the body, with selected ones of the plurality of bores intersecting to produce desired fluid flow channels in a fluid supply and a fluid return circuit in the system. A system with such a monolithic body may be produced with a minimum number of machining operations for economy in manufacture and minimizes fluid leakage.
A further object of the disclosure is to provide valve assemblies for controlling fluid flow in the system, which valve assemblies are operatively mounted in selected one of said bores in the monolithic body.
Yet another object is to provide a novel cushion valve in a fluid control system which produces cushioned starting of fluid flow to moderate acceleration during actuation.
Another object is to provide a novel self-actuating fluid flow rate control valve in a pressurized fluid system operable to advantageously control the rate of fluid flow in the system throughout a wide range of operating conditions.
These and other objects and advantages will become more fully apparent as the following description is read in conjunction with the drawings which are described below.